Heats of formation of (U,Mo)Al3 and U(Al,Si)3

The heats of formation of (U,Mo)Al₃ intermetallic compounds were obtained by measuring the reaction heats of U-Mo/Al dispersion samples by differential scanning calorimetry. Based on literature data for the reaction heats of U₃Si/Al and U₃Si₂/Al dispersion samples, the heats of formation of U(Al,Si)₃ as a function of the Si content were calculated. The heat of formation of (U,Mo)Al₃ becomes less negative as the Mo content increases. Conversely, the heat of formation of U(Al,Si)₃ becomes more negative with increasing Si content.     

Unimolecular isomerization from (CH3)3CNC to (CH3)3CCN induced by infrared free electron laser

Irradiation of IR Free Electron Laser at Tokyo University of Science (FEL-TUS) to t-butyl isonitrile ((CH₃)₃CNC) in the gas phase induced the isomerization reaction to trimethylacetonitrile ((CH₃)₃CCN). From the kinetic analyses, the isomerization reaction was attributed to the IR multiphoton activated unimolecular process. The wide frequency tunability of FEL-TUS enabled us to reveal that the excitation of the NC as well as the CN stretching motion efficiently drove the isomerization.     

离子液体中UO2(CMPO)3(NO3)2的组装及CMPO萃取铀的机理

离子液体具有独特的物理化学性质,可以参与或影响两亲分子自组装。离子液体介质中的自组装研究所涉及的两亲分子多为有机化合物,而金属配合物在离子液体中的组装鲜有报道。另外,萃取剂正辛基苯基-N,N-二异丁基胺基甲酰基甲基氧化膦(CMPO)在1-乙基-3-甲基咪唑双三氟甲基磺酰亚胺盐(C₂mimNTf²)中萃取UO₂⁺²时形成的萃合物结构组成有待深入研究。本工作探究了UO₂(CMPO)₃(NO₃)₂在C₂mimNTf²中的组装行为。原位透射电镜(原位TEM)研究表明:UO₂(CMPO)₃(NO₃)₂在C₂mimNTf²(含70μL水)中形成聚集体,冷冻刻蚀电镜(FF-TEM)显示该聚集体是胶束。此外,研究了CMPO-C₂mimNTf²体系萃取UO₂⁺²时形成的萃合物组成。离子色谱结果表明:萃取前后水相中NO^-₃浓度变化不大,电喷雾质谱(ESI-MS)上均为UO₂(CMPO)₃(NTf₂)₂的碎片离子峰,这些结果说明:CMPO-C₂mimNTf²体系萃取UO₂⁺²时形成的萃合物组成为UO₂(CMPO)₃(NTf₂)₂而非UO₂(CMPO)₃(NO₃)₂。这有助于深入了解金属配合物在离子液体中的组装行为,并对理解CMPO-C₂mimNTf²体系萃取UO₂⁺²的机理提供了重要参考。     

Thermal expansion studies on UMoO5, UMoO6, Na2U(MoO4)3 and Na4U(MoO4)4

In the present work, thermal expansion behavior of lower valent sodium uranium molybdates, i.e., Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were studied under vacuum in the temperature range of 298-873 K using high temperature X-ray diffractometry (HTXRD). Expansion behaviors of UMoO₅ and UMoO₆ were also studied in vacuum from 298 to 873 K and 773 K, respectively. UMoO₅ was synthesized by reacting UO₂ with MoO₃ in equi-molar proportion in evacuated sealed quartz ampoule at 1173 K for 14 h. Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were prepared by reacting UMoO₅ and MoO₃ with 1 and 2 moles of Na₂MoO₄, respectively, at 873 K in evacuated sealed quartz ampoule. XRD data of UMoO₅ and UMoO₆ were indexed on orthorhombic and monoclinic systems, respectively, whereas, the data of Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were indexed on tetragonal system. The lattice parameters and cell volume of all the four compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 873 K.     

The pre-dose effect in natural white mica (H2KAl3(SiO4)3)

A comprehensive study of the pre-dose effect was carried out for natural white mica. A pre-dose of 1 kGy of γ-radiation followed by thermal activation to 550 °C of fired mica (heated at 800 °C for 10 h) leads to a large increase in the TL sensitivity. The TL response to γ-rays of sensitized aliquots was found to be linear-sublinear while that of unsensitized aliquots was linear-superlinear referring specifically to graphs drawn on a linear-linear scale. The change in the TL sensitivity of mica was explained by using the recombination during heating model. This study is of importance in dating and retrospective dosimetry.     

Thermophysical studies on the binary system UO2(NO3)2·6H2O - Sr(NO3)2

Thermoanalytical (TG-DTA-EGA) and X-ray diffraction measurements have been used to study the reaction between uranyl nitrate hexahydrate and strontium nitrate. The results confirmed the absence of a direct interaction between the two compounds. The presence of strontium nitrate, however, ensured that the extent of hydrolysis and polymerisation of uranyl nitrate hexahydrate during its dehydration and decomposition to UO₃ is significantly reduced. DTA curves recorded in both heating and cooling modes gave evidence to the occurrence of a reaction between molten strontium nitrate and uranium trioxide to form nitrato-complexes of uranium and strontium. X-ray diffraction data on reaction residues obtained at different temperatures and cooled to room temperature also showed evidence for the formation of such complexes. The results obtained indicated an increase in thermal stability of these nitrato-complexes with increase in Sr/U ratio. The complex with an Sr/U ratio of 2.0 is stable up to 660 °C and the complex with Sr/U ratio of 4.0 is stable up to 680 °C. These complexes decompose at higher temperatures to give strontium uranates.     

Role of zirconium addition on stability of UAl3 phase in AlU system

The microstructural changes of Al-22 wt%U and Al-46 wt%U alloys containing 3 wt% Zr were investigated after heat treatment at 620°C for 1 to 45 days. Though it is reported that addition of ∼ 3 wt% Zr stabilizes the (U,Zr)Al₃ phase at room temperature, the present investigation shows that the (U,Zr)Al₃ phase is not stable but slowly transforms to the U_0.9Al₄ phase. The high temperature creep curves generated for these ternary alloys showed a wavy pattern which also suggests that the (U,Zr)Al₃ phase is not stable.     

Th(NO_3)_4-UO_2(NO_3)_2-HNO_3-H_2O/30%TBP-正十二烷萃取体系主要组分分配比模型

利用文献报道的Th(NO3)4-UO2(NO3)2-HNO3-H2O/30%TBP-正十二烷体系各组分的分配比实验数据对现有的分配比模型进行分析和比对,提出了一个计算该体系各组分分配比的新模型。利用34组实验数据对新模型进行了验证,符合情况良好。计算结果表明,本文提出的模型明显优于原模型,可作为Th(NO3)4-UO2(NO3)2-HNO3-H2O/30%TBP-正十二烷萃取体系中Th(Ⅳ)、U(Ⅵ)和HNO3萃取行为计算机模拟的基础。模型建立的条件为:温度,25℃;U(Ⅵ)浓度,0~100g/L;Th(Ⅳ)浓度,0~232g/L;硝酸浓度,0~4.5mol/L。     

Preparation and characterisation of Tl2Pu(MoO4)3 and Tl4Pu(MoO4)4 in Tl-Pu-Mo-O system by X-ray and thermal methods

The quaternary Tl-Pu-Mo-O system was investigated for the first time and two new quaternary compounds Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ were synthesized by solid state reactions of Tl₂MoO₄ with Pu(MoO₄)₂ in 1:1 and 2:1 molar proportions at 773 K and 823 K, respectively. X-ray powder diffraction data of these compounds were indexed on orthorhombic system. Thermogravimetric (TG) curves of Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ were recorded in air and no significant weight changes were observed up to 973 K and 1033 K, respectively. Differential thermal analysis (DTA) curves of Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ showed endothermic peaks due to the melting of the compounds at 838 K and 1013 K, respectively. Non-isothermal kinetics of decomposition of Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ in air was studied using thermogravimetric technique. Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ when heated up to 1673 K decomposed to Tl₂O and MoO₃ in the gaseous form, giving solid PuO₂ as an end product. The reactions followed unimolecular nucleation and growth mechanism with activation energies of 106 kJ/mol and 157 kJ/mol, respectively.     

Nd（Fe,Si）11C1．5永磁合金的中子与X射线衍射研究

用中子衍射和X射线衍射技术对配比成分为NdF10.5Si1.5C1.5的永磁合金样品的晶体结构和磁结构进行了研究。测定其为四方的BaCd11型结构,Si元素择优占据8d替代晶位,C原子进入间隙的8c晶位。中子衍射结果表明其磁结构为易面结构。     

Chemical reactions between sodium and (U,Pu)02 mixed oxides

The three phase field MO₂-Na₃MO₄-Na has been studied in detail. It was shown that Na₃MO₄ exists at least in two crystallographic forms and may be above 1200°C, a third one fcc, with a small cell $\text{a = 4.77}\text{A}\text{?}$. This latter form which is considered in the literature as the “normal” uranate cannot be stable in the given conditions of preparation. The low temperature form, simple cubic $\text{a = 9.54}\text{A}\text{?}$, is the one to which the wrong Na₁₁U₅O₁₆ formula has been attributed up to now. It transforms at ca 975°C into a face-centered cubic form with $\text{a = 9.56}\text{A}\text{?}$, stable at least up to 1200°C. Isomorphism between Na-uranate and Na-uranoplutonate has been established for Pu content up to 30%, but there is still some doubt about the nature of the plutonate which is formed by direct reaction between PuO₂ and Na.For the compositions studied (Pu ≤ 30%) the monovariant domain adjacent to the “MO₂”-Na₃MO₄-Na domain, contains the three phases Na₃MO₄, Na₆MO₆ and Na.Oxygen potentials corresponding to the Na₃MO₄-MO_2-x-Na phase field with M = U_0.8Pu_0,2 have been deduced from the measurement of x₀ in equilibrium conditions. It has been foun'd that X_₀ was dependent on T, varying from 0.007 at 550°C to 0.040 at 1200°C. Corresponding values of the oxygen potentials can be represented by the expression: $\text{}\text{?}\text{sm = ? 907, 394 + 224.9 T J/mol 0}{}_2$ A thermodynamic treatment shows that this expression is quasi-independent of Pu content (Pu≤30%) and must be very close to the one valid for the UO₂-Na₃UO₄-Na domain.In conclusion, we examine very schematically how these results can offer guidelines to appreciate the evolution of failed breeder pins in reactor conditions.     

Homogenization in powder compacts of U02-Pu02

The homogenization kinetics in mixed UO₂-PuO₂ compacts have been studied by adopting a concentric core-shell model of diffusion. An equation relating the extent of homogenization expressed in terms of the fraction of UO₂ remaining undissolved and the time of annealing has been derived. From the equation, the periods required at different annealing temperatures to attain a specified level of homogenization have been calculated. These calculated homogenization times have been found to be in fair agreement with the experimentally observed homogenization times. The derived relationship has also been shown to satisfactorily predict homogenization in Cu-Ni powder compacts.     

Rapid synthesis of Pb5(VO4)3I, for the immobilisation of iodine radioisotopes, by microwave dielectric heating

Rapid synthesis of Pb₅(VO₄)₃I, a potential immobilisation host for iodine radioisotopes, was achieved in an open container by microwave dielectric heating of a mixture of PbO, PbI₂, and V₂O₅ at a power of 800 W for 180 s (at 2.45 GHz). The resulting ceramic bodies exhibited a zoned microstructure, differentiated by inter-granular porosity and phase assemblage, as a consequence of the inverse temperature gradient characteristic of microwave dielectric heating. Liquid PbI₂ within the interior of microwave processed ceramics assisted formation of Pb₅(VO₄)₃I, and reduced inter-granular porosity. In contrast, the exterior of microwave processed ceramics comprised poorly sintered Pb₅(VO₄)₃I with the presence of minor reagent relics. Quantitative microanalysis, electron diffraction and Rietveld analysis, confirmed the synthesis of stoichiometric Pb₅(VO₄)₃I within precision. The crystal structure of Pb₅(VO₄)₃I was found to adopt space group P6₃/m with a = 10.4429(3) Å and c = 7.4865(2) Å.     

Decomposition and multiphase reactions in the system UO2(NO3)2·6H2O-Ni(NO3)2·6H2O at elevated temperatures

Solid state reactions between uranyl nitrate hexahydrate and nickel nitrate hexahydrate in mixtures of various ratios have been studied at elevated temperatures. The binary system of uranyl nitrate hexahydrate and nickel nitrate hexahydrate was found to form a eutectic of composition 53 mol% uranyl nitrate hexahydrate and 47 mol% nickel nitrate hexahydrate at 40 °C. The overlap of evolution of nitric oxide (NO) and water vapour above 230 °C confirmed the presence of hydroxynitrates of uranium and nickel as intermediate products. These hydroxynitrates began to react above 280 °C to form nickel uranate, NiU₃O₁₀, in the case of mixtures containing 75 mol% uranyl nitrate hexahydrate. When the proportion of uranyl nitrate hexahydrate in the mixture was higher than 75 mol%, U₃O₈ formed along with nickel uranate. For the mixtures containing uranyl nitrate hexahydrate lower than 75 mol%, NiO was observed to form along with NiU₃O₁₀.     

High-temperature specific heat of UO2 ThO2, and A12O3

The high-temperature specific heat of solid UO₂, ThO₂, and Al₂O₃ can be represented by an equation of the form $\text{C}{}_{\mathrm{p(s)}}\text{= 3}{}_{\mathrm{n}}\text{RF(?}{}_{\mathrm{D}}\text{/T) + dT}{}^3$, (1) where ?_D is the Debye temperature, F(?_D/T) is the Debye function, $\text{d}$ represents contributions of the anharmonic vibrations within the lattice, and $\text{n}$ denotes the number of atoms per molecule. In the liquid the corresponding equation is $\text{C}{}_{\mathrm{p(1)}}\text{= 3}{}_{\mathrm{n}}\text{RF(?}{}_{\mathrm{D}}\text{/T) +}\text{h}\text{T}{}^2$, (2) where h is the anharmonic term. It is shown that for Al₂O₃ and UO₂, where experimental data for the liquid phase are also available, $\text{d}\text{h}$ has the same value, Indicating that both materials behave identically. If we compare the thermodynamic relationship $\text{C}{}_{\mathrm{p}}\text{? C}{}_{\mathrm{v}}\text{= Vα}{}^2\text{KT}$, (3) where V is the volume, $\text{α}$ the volume expansion coefficient, and $\text{K}$ the bulk modulus, with equation (1), It follows that d must be equal to $\text{Vα}{}^2\text{K}\text{T}{}^2$; the value of $\text{Vα}{}^2\text{K}\text{T}{}^2$ is calculated in the temperature region where d was obtained; within experimental error they are equal.     

Properties of lenticular pores in UO2, (U,Pu) O2 and PuO2

Lenticular pore migration rates in oxide muclear fuels were experimentally measured in out-of-pile heating experiments. It is deduced that those pores which are in part responsible for the formation of columnar grains, are only produced in the absence of relevant amounts of filling gas. Specimens containing important concentrations of He, produced by Pu alpha decay, show columnar grain restructuring by grain boundary migration. Some consequences are drawn concerning the possible role played by lenticular pores in the mechanisms of fission gas release from nuclear fuels.     

Thermophysical properties of (U,Y)O2

We prepared polycrystalline pellets of (U,Y)O₂, containing YO_1.5 up to 11 mol.%. We performed indentation tests on the pellets, and evaluated the Young’s modulus and hardness. We measured the heat capacity and the thermal diffusivity, and evaluated the thermal conductivity. We succeeded in evaluating the effect of Y content on the thermophysical properties of (U,Y)O₂. We revealed that the Young’s modulus, hardness, and thermal conductivity of (U,Y)O₂ decreased with increasing the Y content.     

Defect volumes of BO2 doped Y2O3 (B = Ti, Zr, Hf and Ce)

Atomistic simulations have been employed to study the effect of BO₂ (fluorite) incorporation into the bixbyite oxide Y₂O₃. The energetically preferred defect mechanism and the associated lattice parameter changes that occur from BO₂ doping have been predicted. The addition of Group IV elements into Y₂O₃ can follow three different mechanisms. The energetically favourable method is through a mediated reaction for ZrO₂ and HfO₂ while for TiO₂ and CeO₂, reducing B⁴⁺ to B³⁺ provides the lowest energy reaction. ZrO₂ and HfO₂ doping results in the lowest volume changes.     

Thermoluminescence properties of nanocrystalline K2Ca2(SO4)3:Eu irradiated with gamma rays and proton beam

Thermoluminescence properties of nanocrystalline K₂Ca₂(SO₄)₃:Eu prepared by ball milling technique have been studied and the nanophosphor’s suitability as an effective gamma radiation and proton beam dosimeter material has been examined. It is found that the nanophosphor is suitable for dosimetry over a very wide range of doses ∼1 Gy to 1 kGy for gamma radiation. And for proton beam the same nanophosphor shows a more or less linear response for the dose range 0.1-100 Gy. A comparative study of this nanophosphor with its corresponding microcrystalline form (prepared by solid-state diffusion method) as well as the nanocrystalline form prepared by (the more conventional) co-precipitation technique has shown that the nanophosphor prepared by the ball milling technique is in almost all respects better than the other two forms reported earlier.